The present invention relates to the production of noble metal oxalate complexes. Hereinafter, noble metal oxalate complexes shall also be referred to as noble metal oxalates for reasons of simplicity. Specifically, the invention relates to the production of noble metal oxalate complexes from noble metal precursors and oxalic acid and/or oxalic acid salts.
The production of noble metal oxalate complexes from noble metal precursors and oxalic acid and/or oxalic acid salts has been known for a long time. The production of platinum oxalate complexes usually proceeds through the reaction of platinum oxide hydrate (platinum(IV)-hydroxoacid, dihydrogenhexahydroxoplatinate(IV), hydroxoplatinic acid) and oxalic acid at a temperature of 60° C. (K. Krogmann, P. Dodel, Chem. Ber. 99, 3408-3418 (1966)).
EP 0 254 935 A1 describes a method for the production of silver oxalate having a large particle diameter. According to this method, silver salt and oxalic acid or oxalic acid salts are reacted at a pH value of no more than 5. The reaction is carried out at a temperature from 0 to 80° C., preferably at a temperature from 40 to 60° C.
The production of noble metal oxalate complexes from noble metal precursors and oxalic acid and/or oxalic acid salts is an exothermic reaction, in which heat and CO2 are produced. The temperature can increase above the decomposition point of the noble metal oxalate complexes in the course of the reaction, which simultaneously releases more CO2. In this context, see, for example, Sano, Isamu; Bulletin; 15, p. 196, “On the Catalytic Decomposition of Oxalic Acid by Colloidal Platinum” (1940), and Szabó, Z. G. and Biro-Sugar, E., Zeitschrift für Elektrochemie, vol. 50, no. 8, p. 869-874, “Kinetik der thermischen Zersetzung von Silberoxalat” (1956).
For safety reasons, when the reaction is carried out on a large scale, it is therefore necessary to take into consideration that the product must not be decomposed by heat that is produced during the reaction.